The Greenland High, Blocking Patterns and Sandy’s Arctic Arm: How Climate Scientists, Journalists and Bloggers Warned Of New Potential For Extreme Storms Before Sandy

Over the coming weeks, you will hear any number of people trying to ‘normalize’ the unprecedented weather event that was Sandy. You will hear people trying to over-emphasize Sandy’s link to ‘natural climate variability.’ You will hear people claiming that extreme events like Sandy could have never been predicted. And you will hear people trying to take Sandy out of a context in which the US has just experienced its hottest year on record, is still experiencing one of its worst droughts on record, has just experienced its most extreme climate year ever, and during a year in which Arctic Sea Ice has melted to extreme record lows.

And you should be assured — people taking Sandy out of a context of an ongoing string of extreme climate impacts as well as making these other assertions are entirely and completely wrong. Further, it is important to note that we were warned about the increased possibility of extreme storms like Sandy in the weeks and months before Sandy formed.

(Looking at this GOES satellite picture, you can see the swirl of clouds that is Sandy just off the South Carolina coast. See that long arm of clouds stretching down from the Arctic and then feeding into Sandy? That’s Sandy’s Arctic Arm.)

A key ingredient that made Sandy so intense was not just the 5 degree Fahrenheit above average temperatures in the Atlantic Ocean off the East Coast. This five degree warming was fed by an increase of 1 degrees of average Ocean temperature warming over the past century, pushing the potential for extreme years higher. An overall warming directly fueled by human carbon emissions. These increased temperatures and related increases in water vapor fueled Sandy, making her larger and stronger. These were clear global warming impacts that enhanced Sandy’s size and strength. But the kicker, the added boost that made Sandy a monster storm, the influence that pulled Sandy into the East Coast at such a destructive angle. That influence came from the Arctic.

In the GOES image above, we can clearly see a long white arm of cloud stretching all the way down from the Arctic and into Sandy. This arm both greatly increased Sandy’s size and fed her strength through a mechanism called baroclinity. This mechanism fed Sandy’s strength not directly through heat energy alone, but through extreme differences in pressure and temperature. A hot core hurricane met up with a cold core Arctic front tapping the extreme cold air over Greenland. It was this combination of extremes that made Sandy far, far worse. It was this Arctic Arm that pulled Sandy into the East Coast at the most destructive angle possible.

Though scientists didn’t specifically call for the merging of a hybrid system like Sandy, what they did warn us about was how receding Arctic Sea Ice was making severe weather events far more likely. One researcher, Charles Green noted:

“What’s happening now is that we are changing the climate system, especially in the Arctic, and that’s increasing the odds for the negative AO conditions that favor cold air invasions and severe … weather outbreaks.”

Another scientist, Dr. Jennifer Francis also highlighted how Arctic Sea Ice decline would likely result in the kind of blocking patterns that had caused severe weather events in the past. “It’s probably going to be a very interesting winter,” climate scientist Jennifer Francis said in early September in a teleconference with reporters. Francis, a researcher at the Institute of Marine and Coastal Sciences at Rutgers University, has argued that shrinking Arctic ice can be tied to such recent weather events as prolonged cold spells in Europe, heavy snows in the Northeastern U.S. and Alaska, and heat waves in Russia. Francis also noted:

“What we’re seeing is stark evidence that the gradual temperature increase is not the important story related to climate change; it’s the rapid regional changes and increased frequency of extreme weather that global warming is causing. As the Arctic warms at twice the global rate, we expect an increased probability of extreme weather events across the temperate latitudes of the northern hemisphere, where billions of people live.”

Unfortunately, like so many other global warming Cassandras, these warnings went unheeded. A Presidential campaign in which Mitt Romney bragged about denying climate change and de-funding FEMA made mockery of the science and the altogether salient warnings. Such blindness during a year of record drought and Arctic Sea Ice loss is as inexcusable as it is criminal. Such inexcusable piggishness culminated in a Presidential debate in which Romney goaded Obama into arguing over who could increase drilling and, thus, fossil fuel emissions, the most.

Then came Sandy and now all with eyes to see are able to bear witness to both the new potential for extreme weather and its Arctic Sea Ice melt enabler.

(A graphic of the Arctic blocking pattern that resulted in the Greenland High and Arctic air trough that both added strength to Sandy and helped pull her to shore. Image credit here.)

At issue is the way receding Arctic Sea Ice erodes the circumpolar Jet Stream. This happens as warm air is drawn up from the south, slowing that air current down. The result is that huge wave patterns begin to appear in the Jet Stream. These waves draw warmer air up from the tropics in the south and pull cold air down from the Arctic. The blocking pattern also results in a more frequent negative Arctic Oscillation during the fall and winter months. This negative Arctic Oscillation is associated with extreme winter storms in both the US and in Europe and has been implicated in a number of extreme weather disasters over the past decade and a half.

What happened this year is that withdrawing Arctic Sea Ice likely contributed to a very strong negative Arctic Oscillation occurring this fall. The result was a powerful blocking high pressure system over Greenland and an equally strong cold front pushing down from the Arctic. The fact that this happened at the same time Sandy was making her charge north is not simple coincidence. It is, in part, due to the loading of climate dice that resulted from these factors.

First, we had abnormal late-season heat in the Atlantic fueling a powerful late-season hurricane. Second, we had an abnormally strong blocking pattern establishing early during fall rather than winter. The conditions were set for two powerful storms, should they arise, to come together in a dramatic way. The hot Atlantic Ocean was bound to brew up at least a few more hurricanes. Chances were some of these storms would track close to the troughs pushed south by the blocking Greenland high pressure. The receding Arctic Sea Ice was causing more and more strong cold fronts to charge south. Chances were that one of these might intersect with one of the northward-bound tropical systems.

The deep dig of the charging cold fronts and the blocking high closing off any storm’s egress to the northeast made it increasingly likely that any merged hybrid would come ashore somewhere on the US East Coat. The chances for this set of conditions occurring without climate change eroding sea ice and heating the Atlantic are vanishingly small. But now, with the new conditions established, these events become more and more likely.

At issue here is the fact that these conditions are established now. So we can expect an increasing chance for powerful hybrid storms like Sandy resulting from Arctic and tropical storm mergers as time continues, as Arctic Sea Ice melt intensifies, and as the Atlantic Ocean continues to heat up.